Packaged semiconductor device having nanoparticle adhesion layer patterned into zones of electrical conductance and insulation

ABSTRACT

A device comprises a substrate and an adhesive nanoparticle layer patterned into zones of electrical conductance and insulation on top of the substrate surface. A diffusion region adjoining the surface comprises an admixture of the nanoparticles in the substrate material. When the nanoparticle layer is patterned from originally all-conductive nanoparticles, the insulating zones are created by selective oxidation; when the nanoparticle layer is patterned from originally all-non-conductive nanoparticles, the conductive zones are created by depositing selectively a volatile reducing agent. A package of insulating material is in touch with the nanoparticle layer and fills any voids in the nanoparticle layer.

FIELD

Embodiments of the present invention are related in general to the fieldof semiconductor devices and processes, and more specifically to thestructure and fabrication of packaged semiconductor devices havingpatterned conductance single-material nanoparticle adhesion layers.

DESCRIPTION OF RELATED ART

Based on their functions, semiconductor packages include a variety ofdifferent materials. Metals formed as leadframes are employed formechanical stability and electrical and thermal conductance. Insulators,such as polymeric molding compounds, are used for encapsulations andform factors. In packaging fabrication, it is common to attach aplurality of semiconductor chips to a strip of a leadframe to connectthe semiconductor chips to their respective leads and then toencapsulate the assembled chips in packages. The encapsulated packagesprotect the enclosed parts against mechanical damage and environmentalinfluences such as moisture and light. After the encapsulation step, thepackaged chips are separated from the leadframe strip (or packagingsubstrate) into discrete units by a trimming and forming step.

A encapsulation technique is transfer molding method. A leadframe stripwith attached and connected chips is placed into a mold, which forms acavity around each assembled chip. A semi-viscous thermoset polymericcompound is pressured through runners across the leadframe strip toenter each cavity through a gate. After filling the cavities, thecompound is allowed to harden by polymerization. Finally, in thedegating step, the compound in the runner is broken off at each gatefrom the compound filling the cavity.

To ensure the unity and coherence of the package, the metallic andnon-metallic materials are expected to adhere to each other during thelifetime of the product, while tolerating mechanical vibrations,temperature swings, and moisture variations. Failing adhesion wouldallow moisture ingress into the package, causing device failure byelectrical leakage and chemical corrosion.

Today's semiconductor technology employs a number of methods to improveadhesion between diversified materials. Among the methods are chemicallypurifying the molding compounds, activating leadframe metal surfaces forinstance by plasma just prior to the molding process, and enhancing theaffinity of leadframe metals to polymeric compounds by oxidizing thebase metal. Furthermore, design features such as indentations, groovesor protrusions, overhangs and other three-dimensional features are addedto the leadframe surface for improved interlocking with the packagematerial.

Another example of known technology to improve adhesion betweenleadframe, chip, and encapsulation compound in semiconductor packages isthe roughening of the whole leadframe surface by chemically etching theleadframe surface after stamping or etching the pattern from a metalsheet. Chemical etching is a subtractive process using an etchant.Chemical etching creates a micro-crystalline metal surface with aroughness on the order of 1 μm or less. To roughen only one surface ofthe leadframe adds about 10 to 15% cost to the non-roughened leadframe.

Yet another known method to achieve a rough surface is the use of aspecialized metal plating bath, such as a nickel plating bath, todeposit a rough metal (such as nickel) layer. This method is an additiveprocess; the created surface roughness is on the order of 1 to 10 μm.Roughening of the leadframe surface may have some unwelcome sideeffects. General roughening of the surface impacts wire bondingnegatively, since vision systems have trouble seeing the roughenedsurface. The rough surface shortens capillary life, andmicro-contaminants on the rough surface degrades bonding consistency.General rough surfaces tend to allow more bleeding, when the resincomponent separates from the bulk of the chip attach compound andspreads over the surface of the chip pad. The resin bleed, in turn, candegrade moisture level sensitivity and interfere with down bonds on thechip pad.

The success of all these efforts has only been limited, especiallybecause the adhesive effectiveness is diminishing ever more when anotherdownscaling step of device miniaturization is implemented.

SUMMARY

A device comprises a substrate (201) and an adhesive nanoparticle layer(400, 900) patterned into zones of electrical conductance and insulationon top of the substrate surface (201 a). A diffusion region adjoiningthe surface comprises an admixture of the nanoparticles in the substratematerial. When the nanoparticle layer is patterned from originallyall-conductive nanoparticles (302), the insulating zones are created byselective oxidation (500). When the nanoparticle layer is patterned fromoriginally all-non-conductive nanoparticles (1002), the conductive zonesare created by depositing selectively a volatile reducing agent (1200).An insulating material is added to contact the nanoparticle layer andfill pores/voids in the nanoparticle layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the process of creating an additivelayer of electrically conductive nanoparticles and transmuting theelectrical conductance of selected zones to electrical insulatoraccording to an embodiment of the invention.

FIG. 2 is a diagram illustrating the formation of an additive adhesionlayer of electrically conductive nanoparticles according to anembodiment of the invention.

FIG. 3 illustrates an enlargement of a portion of the syringe with anozzle of an inkjet printer, wherein the syringe is filled with a pastemixed with electrically conductive nanoparticles in a solvent accordingto an embodiment of the invention.

FIG. 4 illustrates an additive layer after sintering the electricallyconductive nanoparticles, and after the concurrent diffusion ofmolecules of the nanoparticle material into the subsurface region of thesubstrate according to an embodiment of the invention.

FIG. 5 illustrates the transmutation of the electrical conductance ofselected zones of the sintered nanoparticle layer into electricalnon-conductance, or insulator, by depositing a volatile oxidizing agentaccording to an embodiment of the invention.

FIG. 6 illustrates the completed transmutation in selected zones ofsintered electrically conductive nanoparticles into sinteredelectrically insulating nanoparticles according to an embodiment of theinvention.

FIG. 7 illustrates the encapsulation of the additive layer by apackaging compound, which fills the voids of the additive layeraccording to an embodiment of the invention.

FIG. 8 is a diagram illustrating the process of creating an additivelayer of electrically non-conductive nanoparticles and transmuting theelectrical non-conductance of selected zones to electrical conductanceaccording to an embodiment of the invention.

FIG. 9 illustrates the formation of an additive adhesion layer ofelectrically non-conductive nanoparticles according to an embodiment ofthe invention.

FIG. 10 illustrates an enlargement of a portion of the syringe with anozzle of an inkjet printer, wherein the syringe is filled with a pastemixed with electrically non-conductive nanoparticles in a solventaccording to an embodiment of the invention.

FIG. 11 illustrates an additive layer after sintering the electricallynon-conductive nanoparticles, and after the concurrent diffusion ofmolecules of the nanoparticle material into the subsurface region of thesubstrate according to an embodiment of the invention.

FIG. 12 illustrates the transmutation of the electrical non-conductanceof selected zones of the sintered nanoparticle layer into electricalconductance, by depositing a volatile reducing agent according to anembodiment of the invention.

FIG. 13 illustrates the completed transmutation in selected zones ofsintered electrically non-conductive nanoparticles into sinteredelectrically conductive nanoparticles according to an embodiment of theinvention.

FIG. 14 illustrates the encapsulation of the additive layer by apackaging compound, which fills the voids of the additive layeraccording to an embodiment of the invention.

FIG. 15 illustrates a packaged semiconductor device with leadframe,wherein portions of the leadframe are covered by a nanoparticle adhesionlayer patterned into zones of electrical conductance and insulationaccording to an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In an embodiment of the invention, a method for enhancing the adhesionand mechanical bonding between objects made of diverse materials such asmetals and polymerics is described. The method comprises the formationof an additive adhesion layer composed of intermeshed nanoparticlelayers between the objects. FIGS. 1 and 8 are diagrams illustratingembodiments of the invention. An object, onto which the additive film isconstructed, is herein referred to as substrate, while another object,which needs adhesion to the substrate, is herein referred to as apackage. As examples, a substrate is denoted 201 in FIG. 2, and apackage is denoted 701 in FIG. 7.

Applications of the process shown in FIG. 1 (and in FIG. 8) can beapplied to the fabrication of semiconductor devices. In semiconductortechnology, the substrate typically is either a metallic leadframe or alaminated substrate composed of a plurality of alternating electricallyinsulating and electrically conductive layers. During step 101 of theprocess shown in FIG. 1, a substrate is selected, which is made of afirst material and has a surface.

When the substrate is a leadframe (for example see FIG. 15), theleadframe is usually etched or stamped from a thin sheet of base metalsuch as copper, copper alloy, iron-nickel alloy, aluminum, Kovar™, andothers, in a typical thickness range from 120 to 250 μm. As used herein,the term base metal has the connotation of starting material and doesnot imply a chemical characteristic. Some leadframes may have additionalmetal layers plated onto the complete or the partial surface areas ofthe base metal; examples are plated nickel, palladium, and gold layerson copper leadframes.

A leadframe provides a support pad (1501 in FIG. 15) for firmlypositioning the semiconductor chip (1510). Further, a leadframe offers amultitude of conductive leads (1503) to bring various electricalconductors into close proximity of the chip. Any remaining gap betweenthe tip of the leads and the chip terminals is typically bridged by thinbonding wires (1530); alternatively, in flip-chip technology the chipterminals may be connected to the leads by metal bumps. For theleadframe, the desired shape of pad, leads, and other geometricalfeatures are etched or stamped from the original metal sheet.

Besides chemical affinity between the molding compound and the metalfinish of a leadframe, adhesion may necessitate leadframe surfaceroughness, especially in view of the technical trend of shrinkingpackage dimensions, which offers less surface area for adhesion. Inaddition, the requirement to use lead-free solders pushes the reflowtemperature range into the neighborhood of about 260° C., making it moredifficult to maintain mold compound adhesion to the leadframes atelevated temperatures.

Referring to the process of FIG. 1, during step 102 of the process,layer (designated 200 in FIG. 2) of a solvent paste is deposited ontothe first surface 201 a of substrate 201. The solvent paste comprises asolvent or dispersant including nanoparticles of a second material,which is electrically conductive. An example of the solvent paste isillustrated in FIG. 3 and designated 301. The nanoparticles, dissolvedon the dispersant, are referred to as nanoparticles 302.

Nanoparticles, as used herein, includes spherical or otherthree-dimensional clusters composed of atoms or molecules, of inorganicor organic chemical compounds, of one-dimensional wires, oftwo-dimensional crystals and platelets, and of nanotubes. Furthermore,the surfaces of the nanoparticles may be functionalized againstaggregation, or for improving the adhesion of the nanoparticles. Thefunctionalization can be achieved by attaching ligand molecules to thecore of the nanoparticles. Examples of hydrophobic ligand moleculesinclude trioctylphosphine oxide (TOPO), triphenylphosphine (TPP),dodecanethiol (DDT), tetraoctylammonium bromide (TOAB), and oleic acid(OA). Examples of hydrophilic ligand molecules include mercaptoaceticacid (MAA), mercaptopropionic acid (MPA), mercaptoundecanoic acid (MUA),mercaptosuccinic acid (MSA), dihydrolipic acid (DHLA), bis-sulphonatedtriphenylphosphine (mPEG₅-SH, mPEG₄₅-SH), and short peptide of sequenceCALNN.

The second material may be selected from a group including metals,metallized plastics, and metallized ceramics. The metals may includegold, silver, copper, aluminum, tin, zinc, and bismuth.

During step 103 of the process of FIG. 1, a layer 200 of the solventpaste 301, which includes electrically conductive nanoparticles 302 ofthe second material, is deposited on the surface 201 a of the substrate201 shown in FIG. 2. Surface 201 a is referred to as first surface.Layer 200 may extend over the available two-dimensional surface area, orit may cover only portions of the surface area such as islands betweenabout 0.1 μm to 100 μm dependent on the drop size of the solvent paste.Examples of a few islands are designated 202 and 203 in FIG. 2. Inmetallic leadframes, layer 200 may cover the whole leadframe surfacearea of one or more leads, or selected parts such as the chip attachpad. Building up height from compiled drops of repeated runs of syringe210, layer 200 may preferably have a height 200 a between about 100 nmand 500 nm, but may be thinner or considerably thicker.

The equipment for depositing the solvent paste includes acomputer-controlled inkjet printer with a moving syringe 210 with nozzle211, from which discrete drops 310 of the paste are released. Automatedinkjet printers can be selected from a number of commercially availableprinters. Alternatively, a customized inkjet printer can be designed towork for specific pastes. Alternatively, any additive method can be usedincluding inkjet printing, screen printing, gravure printing, dipcoating, spray coating, and many others.

During step 103 of the process of FIG. 1, energy is provided to elevatethe temperature for sintering together the nanoparticles of the secondmaterial and concurrently for diffusing second material into thesubstrate region adjoining the first surface, thereby anchoring thesintered nanoparticles of the second material to the first surface. Theneeded energy may be provided by a plurality of sources: thermal energy,photonic energy, electromagnetic energy, and chemical energy. Whensintering together, the nanoparticles 302 are necking between theparticles into a liquid network structure 402, as indicated in FIG. 4.The layer 400 of the liquid network structure 402 is electricallyconductive.

Concurrent with the sintering of the nanoparticles 402 of the secondmaterial, some second material is diffusing by atomic interdiffusioninto the first material of the region adjoining the surface 201 a (firstsurface) of substrate 201. The second material diffused into thesurface-near region of substrate 201 does not create electricalconductance in the region adjoining surface 210 a of substrate 201. InFIG. 4, the second material interdiffused into the region near surface201 a of substrate 201 is designated 402 a. The diffusion depth isdesignated 402 b in FIG. 4. The atomic interdiffusion into the substratecreates an interdiffusion bond, which anchors layer 400 of sinteredsecond nanoparticles into substrate 201.

There are several reasons why it may be desirable to transform theelectrical conductance of selected portions of layer 400. As an example,when the conductive nanoparticle layer has poorer adhesion to themolding compound to be employed for the package than a non-conductivelayer (for example, copper nanoparticles compared to copper oxidenanoparticles), and when it is sufficient to use the conductivenanoparticles only where conductive regions of the surface are requiredwhile non-conductive nanoparticles could offer higher adhesion to themolding compound, the net adhesion could be improved by transformingselected regions to the state of electrical non-conductance.

As another example, some circuitry may benefit from local thermalisolation, or electrical isolation, or magnetic isolation for selectedportions of the circuitry. As yet another example, in devices where thesubstrate as well as the package have non-conductive surfaces, selectedtraces of the adhesive and electrically conductive nanoparticle layermay be used for signal routing.

During step 104 of the process of FIG. 1, the electrical conductance ofselected zones of layer 400 is transformed, or transmuted, to electricalinsulator by selective oxidation. As an example, if layer 400 is made ofsintered copper nanoparticles, the nanoparticles of selected zones aretransmuted to copper oxide (CuO, Cu₂O, and other copper oxidationstages).

The most suitable selective technique and equipment may be selected froma group including heating, exposing to oxidizing atmosphere, exposing tooxidizing substances or chemicals, and depositing a volatile oxidizingagent. As an example, the copper nanoparticles of selected traces oflayer 400 may be treated with focused light or laser in an oxidizingenvironment. As another example, the exposure to oxidizing agent may beenabled by masks.

FIGS. 5 and 6 illustrate an example of a selective deposition, ordeposition through a mask, of a chemical agent, followed by evaporationof the agent. In FIG. 5, islands (of lengths 202 and 203) of sinteredelectrically conductive nanoparticles 402 have been formed on surface201 a of substrate 201. In this example, a volatile oxidizing agent 500is selectively deposited in zones designated 511 and 512 of thenanoparticle island of length 202, and zones 521, 522, 523, and 524 ofthe nanoparticle island of length 203. As FIG. 5 shows, oxidizing agent500 is distributed between, and surrounds, the sintered nanoparticles402 of the selected zones. Only certain other zones of the originalconductive nanoparticles 402 remain conductive; in island 202, theremaining conductive zones are designated 202 a, 202 b, and 202 c, andin island 203, they are designated 203 a, 203 b, 203 c. 203 d, and 203e.

In FIG. 6, the transmutation, or transformation, of nanoparticles inselected zones has been completed from the original electricallyconductive characteristic to electrically non-conductive characteristic.The sintered nanoparticles marked 402 are still in their electricallyconductive state, while the sintered nanoparticles 403 in zones 611,612, 621, 622, 623, and 624 are in the electrically non-conductivestate; the nanoparticles in those zones may now be called insulators.The volatile material 500, which served as the oxidizing agent, iseliminated for instance by evaporation. By the selective oxidationprocess, a nanoparticle adhesion layer is created, which is patternedinto contiguous zones of electrical conductance and electricalinsulation.

During step 105 of the process shown in FIG. 1, the solid patternednanoparticle layer, together with at least portions of the substrate 201of first material, are encapsulated into a package of a fourth material,preferably a polymeric compound. The process is illustrated in FIG. 7,wherein the polymeric compound is denoted 701. A method forencapsulation by a polymeric compound is transfer molding technologyusing a thermoset epoxy-based molding compound. Since the compound haslow viscosity at the elevated temperature during the molding process,the polymeric compound can readily fill any pores/voids of the patternednanoparticle adhesion layer. The filling of the pores/voids by polymericmaterial takes place for any pores/voids, whether they are arrayed in anorderly pattern or in a random distribution, and whether they areshallow or in a random three-dimensional configuration includingpores/voids resembling spherical caverns with narrow entrances.

After the compound has polymerized and cooled down to ambienttemperature, the polymeric compound 701 in the package as well as in thepores/voids is hardened. After hardening of the plastic material, thepolymeric-filled pores/voids represent a strong anchor of the package inthe patterned nanoparticle layer, giving strength to the interface ofpackage (fourth material) and the patterned nanoparticle film layer. Inaddition, as mentioned above, the nanoparticle layer is anchored inmetallic substrate 201 by metal interdiffusion 402 a. Together, theoverall adhesion between the plastic package 701 and the metallicsubstrate 201 is improved while the adhesive nanoparticle layer offersselective electrical conductance for signal routing. Adhesionimprovements of an order of magnitude have been measured.

The method illustrated in FIGS. 8 to 14 is another embodiment of theinvention to enhance the adhesion between objects made of diversematerials. The method comprises the formation and anchoring of anadditive nanoparticle adhesion layer between the objects, wherein thelayer includes an array of electrically conductive and non-conductivezones and the application benefits from the better adhesion of theelectrically non-conductive areas. An example is the better adhesion themolding compound of copper oxide nanoparticles compared to metalliccopper nanoparticles. In these cases, it is advantageous to useconductive nanoparticles only where conductive surface zones arerequired, while otherwise non-conductive nanoparticles are employed toenhance the net adhesion across the surface.

During step 801 of the process of FIG. 8, a substrate is selected, whichis made of a first material and has a surface extending in twodimensions; herein, the surface is referred to as first surface. Forsemiconductor devices, the substrate is frequently a metallic leadframeas described above.

During step 802 of the process of FIG. 8, a layer 900 of a solvent pasteis additively deposited onto the first surface 901 a of substrate 901.The solvent paste comprises a solvent or dispersant includingnanoparticles of a second material, which is electricallynon-conductive. An example of the solvent paste is illustrated in FIG.10 and designated 1001. The electrically non-conductive nanoparticles,dissolved on the dispersant, are referred to as nanoparticles 1002 of asecond material.

Nanoparticles includes spherical or other three-dimensional clusterscomposed of atoms or molecules, of inorganic or organic chemicalcompounds, of one-dimensional wires, of two-dimensional crystals andplatelets, and of nanotubes. Furthermore, the surfaces of thenanoparticles may be functionalized against aggregation, or forimproving the adhesion of the nanoparticles of the second material. Thefunctionalization can be achieved by attaching hydrophobic orhydrophilic ligand molecules to the core of the nanoparticles.

The third material may be selected from a group including metal oxides,metal nitrides, metal carbides, ceramics, plastics, polymers, andconducting nanoparticles coated with oxides, polymers, ceramics, andother con-conducting compounds and molecules.

During step 803 of the process of FIG. 8, a layer 900 of the solventpaste 1001, which includes electrically non-conductive nanoparticles1002 of the second material, is additively deposited on thetwo-dimensional surface 901 a of the substrate 901 shown in FIG. 9.Surface 901 a is referred to as first surface. Layer 900 may extend overthe available two-dimensional surface area, or it may cover onlyportions of the surface area such as islands between about 0.1 μm to 100μm dependent on the drop size of the solvent paste. Examples of a fewislands are designated 902 and 903 in FIG. 9. In metallic leadframes,layer 900 may cover the whole leadframe surface area of one or moreleads, or selected parts such as the chip attach pad. Building up heightfrom compiled drops 1010 of repeated runs of syringe 210, layer 900 maypreferably have a height 900 a between about 100 nm and 500 nm, but maybe thinner or considerably thicker.

The equipment for depositing the solvent paste includes acomputer-controlled inkjet printer with a moving syringe 210 with nozzle211, from which discrete drops 1010 of the paste are released.Alternatively, any additive method can be used including inkjetprinting, screen printing, gravure printing, dip coating, spray coating,and many others.

During step 803 of the process of FIG. 8, energy is provided to elevatethe temperature for sintering together the nanoparticles of the secondmaterial and concurrently for diffusing second material into thesubstrate region adjoining the first surface, thereby anchoring thesintered nanoparticles of the second material to the first surface. Theneeded energy may be provided by a plurality of sources: thermal energy,photonic energy, electromagnetic energy, and chemical energy. Whensintering together, the nanoparticles 1002 are necking between theparticles into a liquid network structure 1102, as indicated in FIG. 11.The layer 1100 of the liquid network structure 1102 is electricallynon-conductive.

Concurrent with the sintering of the nanoparticles 1102 of the secondmaterial, some second material is diffusing by atomic interdiffusioninto the first material of the region adjoining the surface 901 a (firstsurface) of substrate 901. In FIG. 4, the second material interdiffusedinto the region near surface 901 a of substrate 901 is designated 1102a. The diffusion depth is designated 1102 b. The atomic interdiffusioninto the substrate creates an interdiffusion bond, which anchors layer1100 of sintered secnd nanoparticles into substrate 901.

During step 804 of the process of FIG. 8, the electrical non-conductanceof selected zones of layer 1100 is transformed, or transmuted, toelectrical conductance by selective reduction or ablation. As anexample, if layer 1100 is made sintered copper oxide nanoparticles orpolymer-coated conductive nanoparticles, the nanoparticles of selectedzones are transmuted by depositing a reducing agent selectively, or byselectively exposing the non-conductive nanoparticles to a reducingatmosphere, for instance formic acid HCOOH, preferably by using a mask.In another method, selective heating may be used to ablatenon-conductive coatings.

FIGS. 12 and 13 illustrate an example of a selective deposition, ordeposition through a mask, of a chemical agent, followed by evaporationof the agent. In FIG. 12, islands (of lengths 902 and 903) of sinteredelectrically non-conductive nanoparticles 1102 have been formed onsurface 901 a of substrate 901. In this example, a volatile reducingagent 1200 is selectively deposited into zones designated 1211 and 1212of the nanoparticle island of length 902, and into zones 1221, 1222,1223, and 1224 of the nanoparticle island of length 903. As FIG. 12shows, reducing agent 1200 is distributed between, and surrounds, thesintered nanoparticles 1102 of the selected zones. Only certain otherzones of the original non-conductive nanoparticles 1102 remainnon-conductive; in island 902, the remaining non-conductive zones aredesignated 902 a, 902 b, and 902 c, and in island 903, they aredesignated 903 a, 903 b, 903 c, 903 d, and 903 e.

In FIG. 13, the transmutation, or transformation, of nanoparticles inselected zones has been completed from the original electricallynon-conductive characteristic to electrically conductive characteristic.The sintered nanoparticles marked 902 are still in their electricallynon-conductive state, while the sintered nanoparticles 903 in zones1311, 1312, 1321, 1322, 1323, and 1324 are in the electricallyconductive state; the nanoparticles in those zones may now be calledconductors. The volatile material 1200, which served as the reducingagent, is eliminated for instance by evaporation. By the selectivereduction process, a nanoparticle adhesion layer is created, which ispatterned into contiguous zones of electrical insulation and electricalconductance.

During step 805 of the process shown in FIG. 8, the solid patternednanoparticle layer, together with at least portions of the substrate offirst material, are encapsulated into a package of a third material. Theprocess is illustrated in FIG. 14, wherein the polymeric compound isdenoted 1401. A method for encapsulation by a polymeric compound istransfer molding technology using a thermoset epoxy-based moldingcompound. Since the compound has low viscosity at the elevatedtemperature during the molding process, the polymeric compound canreadily fill any pores/voids of the patterned nanoparticle adhesionlayer. The filling of the pores/voids by polymeric material takes placefor any pores/voids, whether they are arrayed in an orderly pattern orin a random distribution, and whether they are shallow or in a randomthree-dimensional configuration including pores/voids resemblingspherical caverns with narrow entrances.

After the compound has polymerized and cooled down to ambienttemperature, the polymeric compound 1401 in the package as well as inthe pores/voids is hardened. After hardening of the plastic material,the polymeric-filled pores/voids represent a strong anchor of thepackage in the patterned nanoparticle layer, giving strength to theinterface of package (third material) and the patterned nanoparticlefilm layer. In addition, as mentioned above, the nanoparticle layer isanchored in metallic substrate 901 by metal interdiffusion 1102 a.Together, the overall adhesion between the plastic package 11401 and themetallic substrate 901 is improved while the adhesive nanoparticle layeroffers selective electrical conductance for signal routing. Adhesionimprovements of an order of magnitude have been measured.

FIG. 15 illustrates an embodiment of a semiconductor device 150 usingenhanced adhesion by a nanoparticle adhesion semiconductor layerpatterned into zones of electrical conductance and insulation. Thedevice includes a metallic leadframe and a plastic package wherein theleadframe includes a pad 1501 for assembling a semiconductor chip 1510,tie bars 1502 connecting pad 1501 to the sidewall of the package, and aplurality of leads 1503. The chip terminals are connected to the leads1503 by bonding wires 1530, which commonly include ball bond 1531 andstitch bond 1532. In the example of FIG. 15, leads 1503 are shaped ascantilevered leads; in other embodiments, the leads may have the shapeof flat leads as used in Quad Flat No-Lead (QFN) devices or in SmallOutline No-Lead (SON) devices. Along their longitudinal extension, tiebars 1502 include bendings and steps, since pad 1501 and leads 1503 arenot in the same plane. In other devices, tie bars 1502 are flat andplanar, because pad 1501 and leads 1503 are in the same plane.

In FIG. 15, the portions of the leadframe which are included in thezones of electrical non-conductance of the nanoparticle adhesive layerare marked by dashing 1520. On the other hand, the leadframe portions1503 a included in the zones of electrical conductance are free ofdashing. Since the semiconductor device 1500 includes a package 1570 forencapsulating p 1510 and wire bonds 1530, any pores/voids of thepatterned layer are filled by the polymeric compound. Preferably,package 1570 is made of a polymeric compound such as an epoxy-basedthermoset polymer, formed in a molding process, and hardened by apolymerization process. The adhesion between the polymeric compound ofpackage 1570 and the leadframe is improved by the patterned nanoparticlelayer. Other devices may have more and larger areas of the leadframecovered by the porous bi-layer nanoparticle film.

While this invention has been described in reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications and combinations of theillustrative embodiments, as well as other embodiments of the invention,will be apparent to persons skilled in the art upon reference to thedescription. As an example in semiconductor technology, the inventionapplies not only to active semiconductor devices with low and high pincounts, such as transistors and integrated circuits, but also tocombinations of active and passive components on a leadframe pad.

As another example, the invention applies not only to silicon-basedsemiconductor devices, but also to devices using gallium arsenide,gallium nitride, silicon germanium, and any other semiconductor materialemployed in industry. The invention applies to leadframes withcantilevered leads and to QFN and SON type leadframes.

As another example, the invention applies, in addition to leadframes, tolaminated substrates and any other substrate or support structure, whichis to be bonded to a non-metallic body.

It is therefore intended that the appended claims encompass any suchmodifications or embodiments.

We claim:
 1. A device comprising: a substrate of a first material; a nanoparticle layer on top of and in contact with a surface of the substrate, a region adjoining the substrate surface comprising an admixture of the nanoparticles diffused in the first material; wherein the nanoparticle layer comprises contiguous zones alternatingly having electrical conductance and electrical insulation; and a plastic material making contact with the nanoparticle layer wherein the plastic material fills voids in the nanoparticle layer.
 2. The device of claim 1 wherein the substrate is a laminated substrate including metallic regions.
 3. The device of claim 1 wherein the substrate of the first material is one or more surfaces on a metallic leadframe.
 4. The device of claim 3 wherein the first material of the metallic leadframe is selected from a group including copper, copper alloys, aluminum, aluminum alloys, and iron-nickel alloys.
 5. The device of claim 4 wherein the metallic leadframe further includes plated layers selected from a group including nickel, palladium, gold, and tin.
 6. The device of claim 1 wherein the zones of electrical conductance include nanoparticles having metallic surfaces, the zones of electrical insulation include nanoparticles having oxidized surfaces, and the admixture of diffused nanoparticles includes metals.
 7. The device of claim 6 wherein the nanoparticles having metallic surfaces are selected from a group including metal nanoparticles, metal-coated polymeric nanoparticles, metal-coated ceramic nanoparticles, and metal-coated plastic nanoparticles.
 8. The device of claim 1 wherein the zones of electrical conductance include nanoparticles having reduced surfaces, the zones of electrical insulation include nanoparticles having non-conductive surfaces, and the admixture of diffused nanoparticles includes non-conductive molecules.
 9. The device of claim 8 wherein the nanoparticles having non-conductive surfaces are selected from a group including metal oxide nanoparticles, polymeric compound nanoparticles, nitrogen compound nanoparticles, and electrically conducting nanoparticles coated with polymerics, oxides, and carbon compounds.
 10. The device of claim 1 wherein the plastic material includes a polymeric compound such as an epoxy-based molding compound.
 11. A method for substrate modification comprising: providing a substrate of a first material, the substrate having a first surface; depositing onto the first surface a layer of a solvent paste, the solvent paste including nanoparticles of a second material, wherein the second material is electrically conductive; applying energy to increase the temperature for sintering together the nanoparticles of the second material; transmuting the electrical conductance of selected zones of the layer to electrical insulator by selective oxidation; and encapsulating the nanoparticle layer and at least portions of the substrate in a third material, wherein the third material adheres to at least portions of the nanoparticle layer.
 12. The method of claim 11 wherein the second material is selected from a group including metal nanoparticles, metal-coated polymeric nanoparticles, metal-coated ceramic nanoparticles, and metal-coated plastic nanoparticles.
 13. The method of claim 11 wherein the selective oxidation employs a selective technique chosen from a group including heating, exposing to oxidizing atmosphere, exposing to oxidizing substances, and depositing a volatile oxidizing agent.
 14. The method of claim 11 wherein the selective oxidation by exposing to oxidizing substances employs masking or selective deposition.
 15. The method of claim 11 wherein the third material includes a polymeric compound such as an epoxy-based molding compound.
 16. A method for substrate modification comprising: providing a substrate of a first material, the substrate having a first surface; depositing onto the first surface a layer of a solvent paste, solvent paste including nanoparticles of a second material wherein the second material is electrically non-conductive; applying energy to increase a temperature for sintering together the nanoparticles of the second material; transmuting the electrical non-conductance of selected zones of the layer to electrical conductance by selective reduction or ablation; and encapsulating the layer and at least portions of the substrate in third material wherein the third material adheres to at least portions of the nanoparticle layer.
 17. The method of claim 16 wherein the second material is selected from a group including metal oxide nanoparticles, polymeric compound nanopartricles, nitrogen compound nanoparticles, and electrically conducting nanoparticles coated with polymerics, oxides, and carbon compounds.
 18. The method of claim 16 wherein the selective reduction or ablation employs a technique chosen from a group including selective exposure to reducing atmosphere, selective deposition of a volatile reducing agent, and selective heating for ablating non-conductive coatings.
 19. The method of claim 16 wherein the selective technique includes the use of a mask.
 20. The method of claim 16 wherein the third material includes a polymeric compound such as an epoxy-based molding compound. 